Pneumatic tire and method of designing tread pattern of the tire

ABSTRACT

A pneumatic tire reduces the columnar resonance noise of the tire while controlling the lowering of wet performances, wherein four circumferential grooves continuously extending in the circumferential direction of the tire are disposed in a treading face and a plurality of lateral grooves each having one end opened to the circumferential groove and terminated in a land portion are formed with respect to two circumferential grooves among the four circumferential grooves, and these lateral grooves and the respective circumferential grooves have such a groove width that both groove walls of the groove do not contact with each other in a ground contact face and one or more lateral groove are always completely included in the ground contact face, and an extending length of a portion of each lateral groove in the ground contact face having a groove width of the lateral groove corresponding to not less than 30% of a groove width of the circumferential groove is made not less than 40% of an extending length of the circumferential groove in the ground contact face.

TECHNICAL FIELD

This invention relates to a pneumatic tire effectively reducing a tirenoise, particularly a columnar resonance at a frequency of approximately800-1400 Hz without substantially lowering wet performances of the tireand a method of designing a tread pattern of the tire.

BACKGROUND ART

As the ratio of tire noise occupied in automobile noise becomesrelatively large accompanied with a further improvement of the silencein recent vehicles, the reduction of such a tire noise is a significantmatter. In especial, the tire noise at about 1000 Hz easily hearing withthe human ears becomes a main factor of the off-vehicle noise and theprompt counter-measures with respect to this noise are also demandedfrom a viewpoint of the environmental problems.

In general, it is known that the tire noise at approximately 800-1400 Hzis generated by a columnar resonance resulted from the occurrence of theresonance in an air column defined between a circumferential groove ofthe tire and a road surface in the ground contact face of the tire. Inorder to control such a columnar resonance, it is known that thereduction of the groove volume in the circumferential groove iseffective.

However, the reduction of the groove volume in the circumferentialgroove is obliged to lower the drainage property of the tire and hencethe wet performance thereof. For the purpose of reducing the tire noisewithout lowering the wet performance, for example, JP-A-6-143932proposes a pneumatic tire wherein one wide-width circumferential groovehaving a groove width of 25-70 mm is formed in a central region of thetread and lateral grooves each opening to a ground contact end of thetread but not opening to the wide-width circumferential groove andhaving a groove width corresponding to 5-15% of the wide-widthcircumferential groove are formed at both side portions of thewide-width circumferential groove.

In this proposed tire, however, the large decrease of the ground contactface of the tread necessarily arises because of the existence of thewide-width circumferential groove and also the large stepwise differenceof the ground contact pressure in the widthwise direction of the treadcan not be avoided so that this tire has a problem that it becomesparticularly difficult to simultaneously establish the steeringstability and the limit gripping property on a dry road surface.

The invention is to solve such a problem of the conventional techniqueand to provide a pneumatic tire largely reducing a columnar resonance ofthe tire while attaining the sufficient establishment of the steeringstability and limit gripping property on the dray road surface but alsoeffectively controlling the lowering of the wet performance as well as amethod of designing a tread pattern of the tire.

DISCLOSURE OF THE INVENTION

The invention is a pneumatic tire comprising a tread in which not lessthan two circumferential grooves continuously extending in thecircumferential direction of the tire are disposed in a treading faceand a plurality of lateral grooves, each having one end opened to atleast one predetermined circumferential groove and the other endterminated in a land portion, are independently formed from anothercircumferential groove(s) other than the predetermined circumferentialgroove and another lateral grooves opened to a ground contact end of thetread, and each of the predetermined circumferential groove and lateralgrooves has such a groove width that groove walls do not contact witheach other at a tire posture when the tire is mounted on an approved rimand filled with a maximum air pressure and loaded with a masscorresponding to a maximum load capacity, and at least one of thelateral grooves is always completely included in a ground contact faceof the tread, and an extending length of a portion of each lateralgroove in the ground contact face having a groove width of the lateralgroove corresponding to not less than 30% of a groove width of thepredetermined circumferential groove is made not less than 40% of anextending length of the predetermined circumferential groove in theground contact face.

The term “approved rim” used herein means a rim defined in the followingstandard, the term “maximum air pressure” used herein means an airpressure corresponding to a maximum load capacity defined in thefollowing standard, and the term “maximum load capacity” means a maximummass allowed to be applied to the tire in the following standard.

This standard is determined by an effective industrial standardavailable at an area in which the tires are produced or used,respectively. For example, there are mentioned “Year Book published byThe Tire and Rim Association Inc.” in USA, “Standards Manual publishedby The European Tyre and Rim Technical Organization” in Europe, and“JATMA YEAR BOOK published by The JAPAN AUTOMOBILE TIRE MANUFACTURERSASSOCIATION, INC.” in Japan.

Also, the term “treading face” used herein means a surface region of atread rubber contacting with a flat plate when the tire is mounted thetire on the approved rim and placed vertically on the flat plate underan inflation of the maximum air pressure and loaded with a masscorresponding to the maximum load capacity.

The columnar resonance is generated by oscillating an air column definedbetween the circumferential groove and the road surface in the groundcontact face based on vibration of each part of the tire during therunning to cause a resonant vibration with a wavelength of 2 times thelength of the air column. In this case, a frequency f₀ of the columnarresonance is represented by f₀=v/2L when a sonic speed is v and a groundcontact length in the circumferential direction of the treading face,that is, the length of the circumferential groove included therein is L.

And also, such a columnar resonance results in the occurrence of only acolumnar resonance having one specified frequency in such a treadpattern of the tire that a plurality of circumferential groovescontinuously extending in the circumferential direction of the tread arecommunicated to each other through a lateral groove extended so as tocross with the circumferential grooves.

Moreover, the width, depth and number of the circumferential grooveslargely influence the sound pressure level of the resonance rather thanthe resonant frequency.

As a result of the examinations on the influence of the lateral grooveupon the resonance phenomenon of the circumferential groove, it becomesclear that when the lateral groove is terminated in a halfway of theland portion, the sound is absorbed at a frequency f represented byf=(2n−1)×v/41, wherein 1 is a length of the lateral groove in the groundcontact face, v is a sonic speed and n is an order of vibration (n=1, 3,5 - - - ).

Therefore, when such a sound-absorbing frequency is made close to afrequency of about 800-1400 Hz being the columnar resonance frequency ofthe circumferential groove, it is possible to reduce the resonancenoise.

In addition, it becomes clear that the width, depth and number of thelateral grooves largely affect a sound-absorbing capacity rather thanthe sound-absorbing frequency.

Since the columnar resonance frequency changes within a range of about800-1400 Hz in accordance with the ground contact length of the treadingface, it is required that in order to make the sound-absorbing frequencyto the columnar resonance frequency, the ratio of the extending lengthof the lateral groove included in the ground contact face to the lengthof the circumferential groove is made not less than 40%, morepreferably, not less than 40% but not more than 90%.

When the ratio is less than 40%, the sound-absorbing frequency largelydiffers from a range of the columnar resonance frequency, and hence itis difficult to expect the effective reduction of the resonance noise.

Moreover, in order to sufficiently develop such a sound-absorbingfunction in the lateral groove, it is necessary that the groove walls ofthe lateral groove do not contact with each other in the ground contactface and one or more lateral grooves opened to the predeterminedcircumferential groove are always completely included in the groundcontact face. In this case, the reason why the extending length of thelateral groove is limited to the length of the part of the lateralgroove having a groove width corresponding to not less than 30% of thegroove width of the circumferential groove is due to the fact that whenthe groove width is less than the above, the sound absorbing effect cannot sufficiently be obtained because the groove width of the lateralgroove in the contact with the road surface is narrow and the groovevolume is small.

In addition, the lateral groove having one end opened to thepredetermined circumferential groove and the other end terminated in theland portion is formed without crossing with any of the other lateralgrooves opened to the other circumferential grooves and another lateralgrooves opened to the ground contact end of the tread to control theresonance frequency in the predetermined circumferential groove, wherebythe resonance frequency in a plurality of the circumferential groovesduring the running of the tire under loading can effectively bedispersed, and as a result, the peak level in noise can be reduced andthe change to white noise can largely be promoted as compared with thecase of generating the columnar resonance noise with only the onespecified frequency.

On the other hand, according to the invention, the increase and decreaseof the groove volume in the plural circumferential grooves and the likehave no use for general tires, so that excellent wet performances can berealized while sufficiently establishing both the steering stability andthe limit grip property on the dry road surface without largely changinga basic tone of the existing tread pattern.

In such a tire, the formation of the lateral groove with respect to atarget predetermined circumferential groove can be conducted at only oneside of this circumferential groove but also at both sides thereof. Inany case, the desired function can sufficiently be developed in thelateral grooves opened to the circumferential groove.

When the lateral grooves are disposed at both sides of thecircumferential groove, if all of the lateral grooves are the same size,a larger sound-absorbing effect can be obtained by the increase of thelateral groove number in the treading face as compared with a case offorming the lateral grooves at only one side of the circumferentialgroove. In addition, the lowering of compression and the shearingrigidities due to the increase of the lateral groove number can becontrolled as compared with the case of forming the same number of thelateral grooves at only one side of the circumferential groove, wherebythe deterioration of the steering stability and the like can beprevented.

Furthermore, when at least one sub-groove having one end opened to thelateral groove and the other end terminating in the land portion isformed to the lateral groove while being independently separated fromanother lateral grooves, the wet performances are more improved, andalso it is possible to more reduce the columnar resonance noise becausea sum of the space volumes of the lateral groove and the sub-groove isproportional to the sound-absorbing effect.

In the tire of the invention, two or more of the predeterminedcircumferential grooves opening the lateral grooves can be formed in thetreading face. Even in this case, the same function and effect asmentioned above can be attained by dispersing the resonance frequencywith another circumferential grooves.

In addition, when a plurality of shoulder lateral grooves are disposedso as to extend between each of a pair of another circumferentialgrooves located furthest away from an equatorial line of the tire andeach of the ground contact ends of the tread and opened to both of them,the resonance frequency in these circumferential grooves can be largelyenhanced as compared with that in the above predeterminedcircumferential groove, and hence the effect of dispersing the resonancefrequency is further improved.

In this case, the groove width of the shoulder lateral groove ispreferable to be 1-3 mm in the ground contact face. Thus, the impactsound of the lateral groove on the road surface hardly worsens and theeffect through the dispersion of the resonance frequency can be utilizedat maximum.

When the groove width is less than 1 mm, the effect of dispersing theresonance frequency through the shoulder lateral groove becomesextremely small because the volume of the lateral groove becomes small,and the reduction of the columnar resonance noise is hardly obtained.While, when it exceeds 3 mm, the effect of dispersing the frequencybecomes large, but the impact sound on the road surface and thevibration of the groove wall are increased accompanied with the increaseof the groove width, and the noise level is inversely deteriorated bythe factors other than the resonance.

The method of designing a tread pattern of a pneumatic tire according tothe invention is a method of designing a tread pattern of a pneumatictire in which not less than two circumferential grooves continuouslyextending in the circumferential direction of the tire are disposed in atreading face and a plurality of lateral grooves, each having one endopened to at least one predetermined circumferential groove and theother end terminated in a land portion are independently formed fromanother circumferential groove(s) other than the predeterminedcircumferential groove and another lateral grooves opened to a groundcontact end of the tread, and each of the predetermined circumferentialgroove and lateral grooves has such a groove width that groove walls donot contact with each other at a tire posture when the tire is mountedon an approved rim and filled with a maximum air pressure and loadedwith a mass corresponding to a maximum load capacity, wherein a length lof the lateral groove in the ground contact face under an action of themaximum load capacity is selected so that a frequency represented byf=(2n−1)×v/41 (v: sonic speed, n: order of vibration (n=1)) falls withina range of 800-1400 Hz.

According to this method, as seen from the aforementioned descriptions,the columnar resonance of the circumferential groove can be effectivelyreduced by specifying the required groove width, groove depth and groovenumber under the selection of the length of the lateral groove.

Moreover, the reason for limiting to n=1 is due to the fact that when nis 3, 5 or the like, it is necessary to lengthen the length of thelateral groove to the unattainable degree in the limited land portion.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a developed view of a tread pattern of a pneumatic tireshowing an embodiment of the invention.

FIG. 2 is a view showing a footprint of the tire of FIG. 1.

FIG. 3 is a developed view of another tread pattern.

FIG. 4 is a developed view of the other tread pattern.

FIG. 5 is a view showing a footprint of the other tire.

FIG. 6 is a developed view of a further tread pattern.

FIG. 7 is a developed view of a still further tread pattern.

FIG. 8 is a developed view of a tread pattern of a comparative tire.

FIG. 9 is a schematic view showing a measuring embodiment of the noise.

FIG. 10 is a graph showing a state of a change of the noise level withrespect to a change of the length ratio of the lateral groove.

FIG. 11 is a view showing a footprint of another comparative tire.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention will be explained with reference to theaccompanying drawings below.

FIG. 1 is a developed view of a tread pattern of a pneumatic tireschematically showing an embodiment of the invention.

Moreover, the inner reinforcing structure or the like of this tire isthe same as in a general radial tire, so that the illustration thereofis omitted.

Numeral 1 in this figure is a treading face. In this treading face 1 aredisposed two pairs of circumferential grooves 2, 3 located symmetricallywith respect to an equatorial line C of the tire and continuouslyextending straight in a circumferential direction.

With respect to a pair of center-side circumferential grooves 2 locatedclose to the equatorial line C of the tire among these circumferentialgrooves 2, 3 are disposed a plurality of lateral grooves 5 eachextending in a land portion 4 located at a side opposite to theequatorial line C and having one end opened to the circumferentialgroove 2 and the other end terminated in the land portion 4 so as toextend straight downward to the right in this figure. Each of theselateral grooves 5 is completely independently formed from anotherlateral grooves capable of disposing so as to be opened to anothercircumferential grooves 3.

Also, each of a pair of shoulder side circumferential grooves 3 locatedaway from the equatorial line C of the tire and each of ground contactends E of the tread are communicated with each other by a plurality ofshoulder lateral grooves 6 continuously extending between theshoulder-side circumferential grooves 3 and the ground contact end E andopened to both of them. Moreover, each of the shoulder lateral grooves 6is formed by extending straight in a direction substantiallyperpendicular to the circumferential groove 3.

In the above tread pattern of the tire, under such a state that the tireis mounted on an approved rim and filled with a maximum air pressure andloaded to a mss corresponding to a maximum load capacity, as seen from afootprint of FIG. 2, the groove widths of the circumferential groove 2but also the lateral groove 5 have a size that groove walls of eachgroove do not contact with each other in a ground contact face and anarranging form that one or more of the lateral grooves 5 is alwayscompletely included in the ground contact face. Further, an extendinglength of a portion of the lateral groove 5 having a groove width of thelateral groove corresponding to not less than 30% of a groove width ofthe circumferential groove 2 in the ground contact face, i.e. a wholelength l of the lateral groove 5 shown in FIG. 2 is made not less than40% of an extending length L of the circumferential groove 2 in theground contact face.

According to the tire having such a construction, under the formation ofthe plural circumferential grooves and the like as mentioned above,excellent wet performances can be ensured while simultaneouslyestablishing the steering stability and the limit grip property on thedry road surface, and also the columnar resonance frequencies of therespective circumferential grooves 2, 3 can be made different with eachother. For example, the resonance frequency of the circumferentialgroove 2 can be made considerably small as compared with that of thecircumferential groove 3, whereby the peak level of the columnarresonance noise can effectively be reduced and the change to white noisecan largely be promoted.

FIG. 3 is a developed view showing another embodiment of the treadpattern. In this embodiment, each of lateral grooves 7 having an endopened to the circumferential groove 2 is extended substantially in ahook form and has the other end corresponding to the tip of the lateralgroove 5 added with a bent portion substantially parallel to thecircumferential grooves 2, 3, and the other portions are the same as inFIG. 1.

According to this embodiment, a total length of each lateral groove 7having a sufficient groove width can be lengthened as compared with thatof the lateral groove 5 shown in FIG. 1 and the sound-absorbingfrequency can be approximated to the columnar resonance frequency ascompared with the tire of FIG. 1, so that the resonance noise can bemore effectively absorbed to advantageously reduce the overall level ofthe tire noise.

And also, a crossing angle between the lateral groove 7 and thecircumferential groove 2 can be made larger than that of FIG. 1, so thatthe occurrence of the uneven wear at a corner part of the land portiondefined by these grooves can also advantageously be controlled.

In a tread pattern shown in FIG. 4, a lateral groove 8 opened to thecircumferential groove 2 has a bent portion substantially parallel tothe circumferential grooves 2, 3, an extending length of which is madelonger than that shown in FIG. 3, and a sub-groove 9 having an endopened to the bent portion and the other end terminated in the landportion 4 is disposed so as to extend substantially parallel to aconnecting portion of the lateral groove 8 to the circumferential groove2 without crossing with any grooves.

According to this embodiment, the further improvement of the wetperformance and the more further reduction of the columnar resonancenoise can be realized under a cooperation of the lateral groove 8 andthe sub-groove 9 as previously mentioned.

FIG. 5 is a footprint showing another tread pattern of the tireaccording to the invention, which shows a case that the tire iscontacted with ground under the aforementioned conditions.

In this case, with respect to the pair of center-side circumferentialgrooves 2, lateral grooves 10, 11 respectively extending at both sidesof one circumferential groove are arranged so as to have a tendency ofsubstantially a V-shape as a whole, while they are arranged at the othercircumferential groove 2 so as to have a tendency of substantially aninverted V-shape. Each of the pair of lateral grooves 10, 11 is openedto the circumferential grooves 2 at substantially the same position inthe circumferential direction. Also, each of the lateral grooves 10extending in a land portion 12 located at a center side from thecircumferential groove 2 is formed downward to the right in this figure,while each of the lateral grooves 11 extending in the land portion 4located at a shoulder side from the circumferential groove 2 is formedupward to the right. Further, each of the lateral grooves 11 is providedwith a bent portion extending close to the shoulder-side circumferentialgroove 3 and substantially in parallel thereto.

In this illustrated embodiment, only the shoulder-side lateral grooves11 satisfy a given groove-width condition over approximately a fulllength in the ground contact face and also satisfy a given lengthcondition. Even in such a tread pattern, the resonance frequencies ofthe respective circumferential grooves 2, 3 can be made sufficientlydifferent with each other to effectively develop a desired function ofnoise reduction.

FIG. 6 is a developed view showing the other tread pattern. In thiscase, two pairs of circumferential grooves 2, 3 extend in the zigzagform, and the same lateral groove 8 as described in FIG. 4 is formed bydirectly opening to the center-side circumferential groove 2, and thesub-groove 9 is formed by indirectly opening to the center-sidecircumferential groove 2, and the shoulder lateral groove 6 extendingsubstantially in the widthwise direction of the tread and opened to theground contact end E of the tread is formed by opening to theshoulder-side circumferential groove 3.

Even in this tire, the improvement of the wet performance and thereduction of the columnar resonance noise can be realized under thecooperation of the lateral groove 8 and the sub-groove 9 as previouslymentioned.

FIG. 7 is a developed view of another tread pattern.

In this case, two pairs of circumferential grooves 2, 3 are disposed toextend straight in the circumferential direction, In the land portion 4defined between these circumferential grooves 2 and 3 are formed thelateral groove 8 directly opening to the center-side circumferentialgroove 2 and the sub-groove 9 indirectly opening thereto likewise thecases of FIGS. 4 and 6, while a lateral groove 13 and a sub-groove 14directly or indirectly opening to the shoulder-side circumferentialgroove 3 are formed in a point symmetry with respect to the lateralgroove 8 and the sub-groove 9 therebetween in the land portion 4. Theshoulder-side circumferential groove 3 is communicated with the groundcontact end E of the tread through sipes 15 each extending substantiallyin the widthwise direction of the tread at such a width that the groovewalls contact with each other in the ground contact face.

In this embodiment, as the groove walls of the sipe 15 contact with eachother in the ground contact face, not only the lateral grooves 8 butalso the lateral grooves 13 independently exist from anothercircumferential groove and another lateral groove capable of opening tothe ground contact end of the tread, and can effectively contribute tothe sound absorption together with the respective sub-grooves 9, 14.

Even in such a tread pattern, the approach form of the respectivegrooves into the ground contact face of the tread differs between acombination of the center-side circumferential groove 2, the lateralgroove 8 and the sub-groove 9 and a combination of the shoulder-sidecircumferential groove 3, the lateral groove 13 and the sub-groove 14,and the columnar resonance frequencies in the respective groove portionsincluding the respective circumferential grooves 2, 3 also necessarilydiffer, so that the required dispersion in the resonance frequencies iseffectively conducted.

EXAMPLES Example 1

At a state of mounting an example tire having a tire size of 195/65 R15on a rim of 6J, filling with an air pressure of 220 kPa and applying aload of 4.25 kN, the columnar resonance noise level (1000 Hz) and theoverall level of the noise are measured at a speed ranging from 40 km/hto 100 km/h every 10 km/h according to JASO C606 standard, and theresistance to hydroplaning in the actual straight running is evaluatedby entering a vehicle into a road surface having a water depth of 10 mmto measure a vehicle speed floating the tire.

The average values of these measured results are shown in Table 1.

In Table 1, Example tire 1 has a tread pattern shown in FIG. 1, andExample tire 2 has a tread pattern shown in FIG. 2 and Example tire 3has a tread pattern shown in FIG. 4. On the other hand, Comparative tire1 has a tread pattern shown in FIG. 8 in which all of the lateralgrooves and the shoulder lateral grooves opened to the ground contactend of the tread are opened to the shoulder-side circumferential groove.

In the measurement of the noise, as shown by a side view in FIG. 9, fivemicrophones are arranged not only at a measuring position defined inJASO C606 but also at positions set every 50 cm within a range of 1 mforward and backward from the above measuring position, and the noiselevel is determined by calculating an average value from the measuredwaveforms.

TABLE 1 Comparative tire 1 Example tire 1 (FIG. 8) (FIG. 1) Columnarresonance noise level control −1.6 dB (A) (1000 Hz) Overall levelcontrol −0.7 dB (A) Resistance to hydroplaning 100 100 (Index) * Exampletire 2 Example tire 3 (FIG. 3) (FIG. 4) Columnar resonance noise level−1.9 dB (A) −3.0 dB (A) (1000 Hz) Overall level −0.8 dB (A) −1.0 dB (A)Resistance to hydroplaning 100 100 (Index) * * Index value shows thatthe larger it becomes, the more excellent the result is.

As seen from Table 1, all Example tires can advantageously reduce thenoise while effectively controlling the lowering of the wet performanceand also the effect of reducing the noise is improved in accordance withthe increase of the length of the lateral groove

Example 2

Next, the change of the overall level in the noise and the change of thecolumnar resonance are measured in the same manner as mentioned aboveunder the same conditions as in Example 1 using the ratio of the lateralgroove length to the circumferential groove length in the ground contactface to obtain the effect shown by a graph in FIG. 10.

As seen from FIG. 10, the noise level violently lowers when the ratio ofthe lateral groove length is more than 40%.

Example 3

At a state of mounting an example tire having a tire size of 195/65 R14on a rim of 6J, filling with an air pressure of 200 kPa and applying aload of 4.9 kN, the columnar resonance noise level (1000 Hz) and theoverall level of the noise are measured at a speed of 80 km/h in thesame manner as in Example 1, and the resistance to hydroplaning in thestraight running is also evaluated in the same manner as in Example 1.

The average values of these measured results are shown in Table 2.

In Table 2, Example tire 4 has a footprint (I/L=0.4) shown in FIG. 5 andComparative tire 2 has a footprint shown in FIG. 11.

TABLE 2 Comparative tire 2 Example tire 4 (FIG. 11) (FIG. 5) Columnarresonance noise level 80.2 dB (A) 78.9 dB (A) (1000 Hz) (−1.3) Overalllevel 86.5 dB (A) 86.0 dB (A) (−0.5) Resistance to hydroplaning 100 100(Index) * * Index value shows that the larger it becomes, the moreexcellent the result is.

As seen from Table 2, the noise level can be reduced without loweringthe wet performances, especially a hydroplaning property in question.

INDUSTRIAL APPLICABILITY

As seen from the above examples, according to the invention, the noisesgenerated in the tire, particularly columnar resonance can beeffectively reduced while sufficiently highly ensuring the wetperformances of the tire.

1-8. (canceled)
 9. A pneumatic tire comprising a tread, said treadcomprising: at least one first circumferential groove, said at least onefirst circumferential groove which extends continuously in thecircumferential direction of the tire and which is disposed in atreading face; at least one second circumferential groove, said at leastone second circumferential groove which extends continuously in thecircumferential direction of the tire and which is disposed in thetreading face; a first plurality of lateral grooves, each of the firstplurality of lateral grooves having a first end opened to the at leastone first circumferential groove and each of the first plurality oflateral grooves having a second end, which terminates in a land portion;wherein each of the first plurality of lateral grooves is formedindependently of a second plurality of lateral grooves, each of saidsecond plurality of lateral grooves opened to the at least one secondcircumferential groove and not opened to the at least one firstcircumferential groove, the second plurality of lateral groovesincluding shoulder lateral grooves opened to a ground contact end of thetread, wherein said at least one first circumferential groove isseparated from said at least one second circumferential groove and saidat least one first circumferential groove is formed independently of thesecond plurality of lateral grooves, wherein each of the at least onefirst circumferential groove and the first plurality of lateral grooveshas a groove width such that groove walls do not contact with each otherat a tire posture when the tire is mounted on an approved rim and filledwith a maximum air pressure and loaded with a mass corresponding to amaximum load capacity, and wherein a length l of the lateral groove inthe ground contact face under an action of the maximum load capacity isselected so that a frequency represented by f=(2n−1)×v/41 (v: sonicspeed, n: order of vibration (n−1)) falls within a range of 800-1400 Hz.10. A pneumatic tire according to claim 1, wherein sipes which areopened to at least one of the first and second circumferential groovesat a width such that groove walls contact with each other in the groundcontact face, said sipes formed independently of any of the first andsecond pluralities of lateral grooves.